1. Field of the Invention
The present invention relates to an image formation apparatus such as a copier, fax machine, or printer, and more particularly relates to a fixing apparatus that melts and solidifies toner on a recording medium such as recording paper or OHP film.
2. Description of the Related Art
In the fixing step with this type of image formation apparatus, a toner image on a recording medium that has been transferred from a photosensitive member (latent image support) is fixed on a recording medium, and this is an essential step in which, for example, toner is put in a molten state by heating and pressing, and the toner is made to permeate and fuse to transfer paper, a resin sheet, or another such recording medium in this molten state. Fixing methods include contact fixing methods in which the members on the heat source side are in direct contact with the toner (what is being fixed), and non-contact methods which involve atmospheric heating by ultraviolet rays or inductive heating. Typical contact fixing methods are heat roller fixing methods and belt fixing methods. With the fixing apparatus used in all of these contact methods, a nip is formed at a location where there is contact with the roller and/or belt, the recording medium is conveyed so as to be heated and pressed in this nip, and this fixes the toner to the recording medium. The heating and pressing are accomplished by bringing the toner into direct contact with a heated belt or a fixing roller equipped with an internal heat source such as a halogen lamp or a nichrome wire, thereby fixing the toner. With this fixing apparatus, the heat source is managed by a temperature sensor provided to the roller or belt surface so that the surface is kept at a specific temperature, and this stabilizes the amount of heat supplied to the sheet passing through the nip.
There has been demand in recent years for lower energy consumption and shorter standby times. However, if the temperature during standby is lowered, it takes longer for warm-up, which is how long it takes for the fixing apparatus to rise to the temperature at which fixing is possible, and this lowers fixing efficiency. Consequently, in an effort to reduce the thermal capacity of a fixing apparatus, fixing belts have come to be used rather than a fixing roller. Switching to a fixing belt speeds up the rise in temperature of the fixing apparatus, which shortens the warm-up time and helps conserve energy. With a fixing apparatus equipped with a fixing belt, the heating roller is warmed by heat generated from a heater or the like, and this heat is transmitted to the belt, which supplies heat to the nip where the unfixed toner image is fixed.
When a thin heating roller is used in order to speed up the warm-up process, heat moves to the belt and ends up being radiated while the heating roller is in the course of reaching its set temperature, and this makes it take longer for the heating roller to reach its set temperature.
In view of this, with the prior art disclosed in Japanese Laid-Open Patent Application H6-148856, this movement of heat is curbed by loosening the temperature of the belt on the heating roller. When the tension is loosened, though, a few seconds are lost when the tension is reapplied, so despite the effort to minimize the excess radiation of heat, time is spent reapplying tension, so at present there is little merit to accelerating the warm-up process.
Technologies relating to the present invention are (also) disclosed in, e.g., Japanese Laid-Open Patent Applications 2001-20966 and 2002-251089.